1. Field of the Invention
The present invention relates to an electric dust-collection unit, and method of manufacture, together with an air-cleaner, electric dust-collection device and exhaust smoke removal device employing that unit.
2. Description of the Prior Art
The increasingly air-tight construction of offices, restaurants, technical installations, homes and other buildings (hereinafter referred to representatively as `offices`) of recent years has not only meant that air contaminated with dust (suspended particulates) from cigarette smoke, toner, paper and other sources, foul odours and similar harmful substances exercises a detrimental effect on the health of persons working in the offices, but has led to a high incidence of soiling of equipment and machinery.
The conventional method of dealing with this problem in offices has been to install ventilation fans in places such as smoking-rooms where the contamination is obviously high, thus expelling the contaminated air from the room. However, this method suffers from the disadvantage that the temperature inside the room is affected by the temperature outside it, resulting in a considerable deterioration in the efficiency of heating and cooling. In order to maintain a constant temperature within the room while at the same time purifying the air, not only must the ventilation fan be operated continuously, but it is necessary also to operate the air-conditioner to heat or cool as required. This is undesirable because of the vast amounts of electricity which air-conditioners and ventilation fans consume.
It is in these circumstances that electronic air-cleaners employing electric dust-collection devices have come into their own as being capable of operating with minimal ventilation, thus eliminating the wastefulness of the air-conditioner and offering considerable savings in terms of the amount of electric power which they consume.
An example of a conventional air-cleaner of this sort is illustrated in FIGS. 19 and 20. It is designed to be hung on the wall, and consists in the main of a suction member 3, whereby the contaminated air 2 within a room is sucked in through the aperture 1, a pre-filter 4, an electric dust-collection unit 5, a deodorising filter 6 comprising activated carbon fibres, a dust-collection member 7 wherein dust and odours are eliminated from the air which passes through it, an expulsion member 9 fitted with louvres through which air 8 which has been purified in the dust-collection member 7 is expelled from the room, and a power supply member which is not shown in the drawing. The abovementioned expulsion member 9 is fitted with an electrically operated fan 10, whereby contaminated air 2 is sucked in through the aperture 1, and after being purified in the dust-collection member 7, is expelled as clean air 8 through the expulsion member 9. This air-cleaner is configured in such a manner that the suction member 3 protrudes along the surface of the ceiling, thus making it possible for the air within the room to circulate efficiently, as a result of which it is purified instantly. The front plate of the dust-collection member 7 comprises a door 11 which can be lowered in order to allow the pre-filter 4, electric dust-collection unit 5 and deodorising filter 6 to be removed, cleaned and re-inserted so that they can be used time and time again.
With reference to FIGS. 21-25 there now follows a detailed description of the electric dust-collection unit 5, which forms the most important part of the air-cleaner.
FIG. 21 is a longitudinal cross-section illustrating the structure of the electric dust-collection unit; FIG. 22 is a longitudinal cross-section showing the electric dust-collection unit separated into sub-units; FIG. 23 is an oblique view of the electric dust-collection seen from the front (the side from which the air is sucked in); FIG. 24 is an enlarged oblique view of part of FIG. 23; and FIG. 25 is an oblique view of the electric dust-collection seen from the rear (the side on which the air is expelled). As these drawings show, the abovementioned electric dust-collection unit consists of needle electrodes 12 shaped like gramophone needles, which form ionisation space areas, and deflecting electrodes 13 shaped like rectangular columns approximately 10 mm square and 5-6 cm in length, which support and hold the needle electrodes 12 firm and from the leading surface of which they protrude. The two together form composite needle and deflecting electrodes 14, which are arranged vertically and horizontally in the form of a lattice. The composite needle and deflecting electrodes 14 are arranged in such a manner that collector cells (electrodes which attract and collect dust and other particulates by means of static electricity) 15 in the shape of hollow rectangular tubes approximately 20 mm square and 5-6 cm in length are inserted between each of them so as to create a rectangular gap of approximately 5 mm around them, this acting as a passage for the air. As FIG. 22 shows, the male sub-unit 16 and the female sub-unit 17 can be separated in order to facilitate cleaning.
The male sub-unit 16 has a box-shaped frame (hereinafter referred to as the `outer box frame`) 18, to the lower surface of which are joined by way of insulating plates 20 supporting members 19, which support a large number of composite needle and deflecting electrodes 14 and are linked to one another so as to be equipotential, the large number of composite needle and deflecting electrodes 14 being arranged in lattice shape on the inside of the outer box frame 18. The female sub-unit 17 also has a box-shaped frame (hereinafter referred to as the `inner box frame`) 21, on the inside of which are formed in a lattice shape a large number of the collector cells 15. When the device is in operation, a high voltage (5-6 kV) is impressed from a high-voltage direct-current power source not shown in the drawings so that the composite needle and deflecting electrodes 14 and the collector cells 15 are connected in such a manner that the former has positive and the latter negative potential. As FIGS. 23 and 24 show, the outer box frame 18 of the male sub-frame 16 and the inner box frame 21 of the female sub-frame 17 fit into one another so that each of the composite needle and deflecting electrodes 14 corresponds in arrangement to one of the collector cells 15, which is to say, so that each composite needle and deflecting electrode 14 is inserted into a collector cell 15 without coming into contact with it.
FIG. 26 illustrates the action of the air-cleaner.
As will be seen from FIG. 26, when in the abovementioned configuration a high direct-current voltage is applied to the composite needle and deflecting electrodes 14, a sort of corona discharge occurs around the tip of the needle electrodes 12. The discharge is sustained and stable, and leads to the formation of an ionisation space area 22. When the contaminated air 2 sucked into the suction member 3 by means of the electrically operated fan 10 now passes through the ionisation space area 22, the oxygen, being low in ionisation energy, undergoes electrolytic dissociation into positive ions. These adhere to particulates 23 in cigarette smoke and other contaminants, which themselves receive the electric charge of the positive ions. When the charged particulates 23 then pass through between the deflecting electrode 13 and the collector cell 15, those which are close to the collector cell 15, which has a negative potential, adhere to it. Meanwhile, those particulates 23 which are at a distance from the collector cell 15 are repelled by the positive potential of the polar plate of the deflecting electrode 13 in the direction of the collector cell 15, to which they adhere. In this manner, it is possible to implement effective dust collection from small particulates of approximately 0.01 .mu.m in diameter to relatively large ones of around 10 .mu.m.
As is shown in FIG. 27 (a), the needle electrodes 12 consist of a pin member 120 of stainless steel or a similar material with a nickel-plated tip. Meanwhile, the deflecting electrodes 13 consist of pairs of plate electrode members 130 of stainless steel or a similar material, which are folded into the shape of a valley with a flat bottom and sides at right-angles to it. These are placed together, with their open sides facing each other and their corresponding ends matching, so as to form a rectangular pillar shape. Hitherto, as FIG. 27 (b) demonstrates, it has been common practice when producing the composite needle and deflecting electrodes 14 and after placing a pair of folded plate electrode members 130 on top of each other to form a rectangular pillar, to fit the base of the pin member 120 against the joint on their leading edge, and secure the vicinity of the point of contact between the pin member 120 and the two folded plate electrode members 130 with silver solder 24, thus fashioning the deflecting electrode 13 and integrating it with the pin electrode 12 at the same time. However, it is normal to find some 100 composite needle and deflecting electrodes mounted on one electric dust-collection unit 5, for which reason the conventional method of production using silver solder 24 requires a great deal of work and time to be expended on it. Consequently, there has been a problem of cost-effectiveness in that while air-cleaners of the needle discharge type present the technical advantage of more powerful dust collection, there has been no way of reducing costs and rendering mass-production feasible.
On the other hand, the simpler configuration of lattice-shaped collector cells 15 illustrated in FIG. 28, wherein a set of metal plates 150 (hereinafter referred to as `cell electrode plates`) of stainless steel or a similar material having numerous equidistant slit-shaped notches 25 (hereinafter referred to as `notch slits`) are successively interlocked at the notch slits 25 from above and below at right-angles, facilitates mass-production, but is fraught with the problem that since the cell electrode plates 150 are thin, they are liable to become deformed as a result of accidental external forces acting on them during manufacture or transport, effective dust collection being reduced considerably where such deformation (indicated on the drawing by the symbol A) occurs.